This is my idea of a pec minor stretch. In front of the edge of a wall, in a right stride stance, do a RUE L45 reach @ thigh height. From there do a thumb down R120 reach @ shoulder height. As you do the reach, attempt to tap the R AC joint to the wall the best you can. Hold for 2 seconds @ return to the starting position for 3 sets of 10.
The right stride stance will block rib rotation so that the origin of the pec minor is being lengthened in all 3 planes. The AC joint tap on the wall requires the lower traps to glide the scap caudally. The pronated hand reach shortens the pec major, lengthening the insertion of the pec minor in all 3 planes.